If you're thinking of trying to make an environmental difference in your house with some renovations or technical solutions your first action does not necessarily have to be expensive or highly technical. Existing houses generally have major 'gaps' in their structures, walls, windows, etc which let air in and out of your building. If you apply sealant or products that block these drafty locations your building envelope will be more efficient and your energy consumption to maintain a comfortable environment in your house will be reduced. This a cheap, non-technical solution that can make a significant difference to your household budget and your environmental footprint!
How do you know where the air is escaping from your house? I heard someone suggest a fog machine. What a funny, clever idea! The principle is to close your house up, turn the fog machine on inside and then stand outside and watch the house to see the locations where the fog is escaping. Places like under the doors and window frames are obvious locations to look for gaps and easily addressed.
I now just have to get onto a rental company to hire one of these machines or find someone who has one left over from the 90s. Or perhaps just feeling where the cold air comes into the house as a draught in the evenings is an easier, less onerous process but surely not as fun!